This invention relates to gas turbine engine cooling systems.
In order to increase the efficiency and specific power output of gas turbine engines, these engines are designed to operate at ever increasing turbine inlet temperatures. To enable operation at such elevated temperatures, various engine components, such as the turbine nozzles and blades are cooled by a flow of coolant, typically high pressure bleed air from the turbine engine compressor. The high pressure air is diverted from the compressor discharge upstream of the burner and routed directly to the turbine blades and vanes, where it is discharged from openings in the turbine blades and nozzles to reduce the surface temperature of these components. However, coolant flow is a parasitic flow loss reducing engine efficiency.
At high power settings, such as during takeoff, the amount of cooling air that is required is relatively high. At lower power settings such as at cruise or idle, however, there is relatively little cooling air required. Nevertheless, conventional coolant flow systems are generally fixed in capacity to provide sufficient coolant flow to maintain the turbine blades and vanes below their design temperature when the turbine is operating at its maximum rated power. Accordingly, at reduced power settings, the flow of coolant is in excess of that necessary to maintain component temperature. This excess coolant flow results in engine efficiency below that which could be achieved if the bleed air were regulated to respond to the engine power requirements.
Regulation of coolant flow in response to engine operating conditions has been recognized as desirable. For example, U.S. Pat. No. 4,217,755 to Williams teaches a coolant flow valve in which a valve member regulates the flow of coolant in response to engine temperature. The opening and closing of the valve member is, however, controlled by an external controller, with commensurate complexity and reliability issues. U.S. Pat. No. 4,296,599 teaches a plurality of normally closed valves that open to permit a flow of coolant in response to an increase in the gross coolant air pressure or coolant air temperature. None of the prior art coolant systems, however, provide a simple passive feedback control of coolant flow that is responsive to engine coolant flow requirements.